1. Field of the Invention
The present invention relates to a method for producing an LED (light emitting diode), and more particularly to a method for producing a high brightness LED, in which excellent mechanical strength for manufacturing can be exhibited.
2. Related Prior Art
Currently, how to promote the brightness or illuminence is a significant issue for developing LED (light emitting diode). Therefore, many studies and developments are being made by researchers and industries.
As one of the most useful substrates for manufacturing LED, GaAs is still not satisfying enough in emitting efficiency, because partial wavelength will be absorbed. R.O.C. Pat. No. 385557, 391067 and 332344 mentioned solutions of this problem by forming epitaxial films with functions of conduction or reflection on the substrate. However, such design is still not satisfying for achieving high brightness.
U.S. Pat. No. 5,376,580 mentioned another solution, in which the GaAs substrate is removed after a transparent GaP substrate is bonded to the LED epitaxial layers formed on the GaAs substrate. In this method, an epitaxial layer of 60–70 μm needs to be processed, and the alignment with crystal axes of the GaP substrates is difficult during the wafer bonding process. On the other hand, the thermal treatment for a long time may influence luminous effect of the LED with p-n or n-p junction.
R.O.C. Pat. No. 415116 also provided a structure, in which a reflective layer and an adhesion layer are formed between the LED epitaxial layers and the conductive substrate. While such design facilitates brightness of the LED, the following problems exist:
1) The substrate tends to be damaged caused by thermal stress due to different heat transfer coefficients and different thermal expansion coefficients between the layers. For example, the heat transfer coefficient of silicon triples that of GaAs, but the thermal expansion coefficient of silicon is less than that of GaAs (Si: 2.6×10−6/K, GaAs: 5.7×10−6/K). Therefore, the Si substrate or GaAs or both may be broken during thermal process.
2) Reflectivity of the reflective layer or characteristic of the light emitting diode may regress because of mutual diffusion between the layers and the substrate.
Therefore, it is desirable to provide an improved LED structure to mitigate and/or obviate the aforementioned problems.